1. Field of the Invention
This invention relates to a displacer-type Stirling engine such as a free-piston Stirling generator, a compressor, a pump or an engine, in which a displacer is driven by a motor.
2. Description of the Prior Art
A Stirling engine is known in which a cam is driven by a motor, a displacer piston is reciprocated by the cam via a displacer rod, and a free power piston is reciprocated by the displacer piston. A method of reducing motor power in an engine of this type has been proposed by the applicant but has not yet been disclosed publicly. In the proposed method, mechanical springs or gas-operated springs, or a combination thereof, are disposed above and below the cam to construct an oscillatory system in which the differential between the fluctuating pressure in a working space and the static pressure in a crank chamber is used as an external force to act upon the displacer rod.
With this method, the force which acts upon the displacer rod owing to the fluctuating pressure of the working gas and the static pressure of the crank chamber is utilized effectively as auxiliary power. An additional aim is to reduce loss attributed to surface pressure caused by inertial force. Since springs are installed that are capable of reducing motor driving power when the displacer piston is reciprocated, a high torque is needed in order to compress the springs at starting of the motor. Though net efficiency is raised, a problem encountered is that the motor must be large in size. This runs counter to a reduction in the size of the apparatus.